Pd-based Noble-catalyst Supported On Y Molecular Sieve For Catalytic Degradation Of Toluene

Last few years,a large number of ecological problems such as air pollution,soil pollution and water pollution caused by volatile organic pollutants(VOCs)have become increasingly prominent,and the degradation of VOCs cannot be delayed.Compared with other technologies,the catalytic oxidation method is favored by people in the treatment of VOCs because of its advantages such as low energy consumption,no secondary pollution,and rapid and efficient degradation of pollutants at a lower operating temperature.Research and development of low-load,high-activity,high-stability catalysts is the key to this treatment technology.Supported noble metal catalysts have the advantages of low light-off temperature,high catalytic activity,and fewer degradation by-products,and are very suitable as catalyst active component materials.Y molecular sieve has the advantages of high specific surface area and high hydrothermal stability,and its faujasite cage structure can realize orderly encapsulation of active components,so that noble metals can stably exist in the molecular sieve in a highly dispersed state.In this paper,Y molecular sieve is used as the support,and Pd is introduced into the Y molecular sieve cage by ion exchange method.After roasting,ethylene glycol or hydrogen is used as a reducing agent to realize the orderly "encapsulation" of the catalytic active center Pd in the Y molecular sieve α cage and β cage,to investigate its adsorption performance and catalytic activity to toluene,and the following conclusions were reached:(1)The metal active component Pd is introduced into the super cage of NaY molecular sieve by ion exchange method.After roasting,the active component migrates to the sodalite cage,and then the sodium sulfate is reduced by the ethylene glycol reduction method and the hydrogen reduction method.The metal activity in the gabion is reduced.Through a series of characterizations,it is found that Pd finally exists in the Y molecular sieve cage in the form of Pd0 as the main active site for the catalytic oxidation of toluene.The calcination temperature will affect the decomposition of the precursor Pd(NH3)42+ and regulate the position of the active component Pd in the molecular sieve.The results show that the increase in temperature is conducive to the migration of Pd to the βcage.(2)During the ethylene glycol reduction process,the content and dispersion of the active component PdO can be adjusted by changing the solution pH,reduction temperature,reduction time and load.The results show that the catalyst prepared when the solution pH=5,the reduction temperature=160℃,and the reduction time is 6h has the highest catalytic activity for toluene.The content of Pd0 and the degree of dispersion of Pd in the molecular sieve will affect the catalytic activity of the catalyst to toluene.The thermal reduction of hydrogen easily leads to the migration and agglomeration of active components,so that the dispersion of Pd and the content of Pd0 in the catalyst prepared by the ethylene glycol reduction method are far better than that of the hydrogen reduction,and therefore,it exhibits higher catalytic activity.Hydrogen thermal reduction easily leads to the migration and agglomeration of active components,while the glycol reduction method is beneficial to the dispersion of Pd in the catalyst and the content of Pd0 is much better than hydrogen reduction,therefore,it shows higher catalytic activity.(3)The catalytic reaction process of the catalyst to toluene follows the L-H mechanism.The specific reaction process is as follows:First,toluene is adsorbed on the surface of the molecular sieve and in the supercage,and oxygen is converted into active oxygen species under the action of the active sites on the surface of the molecular sieve,the supercage and the sodalite cage,and then interacts with the adsorbed Toluene interacts and oxidizes it to CO2 and H2O.